1. Field of the Invention
This invention relates generally to a numerical control system for machines and, more particularly, to a numerical control system with a programmable sequence controller for effecting the transmission of various control data between a digital computer and a plurality of numerically controlled machines governed by the computer.
2. Description of the Prior Art
In general, in a direct control system using a computer to control numerically controlled machine tools, there has been extensively adopted a system with so-called BTR-adapters 4, 4, as shown in FIG. 1. In this system, numerical control data are supplied through the BTR-adapters 4, 4, each serving as a data link device, not from tape readers 6, 6 of numerical controllers 2, 2, but from a central computer 1. The numerical control data supplied through the BTR-adapter 4 is decoded in the numerical controller 2, roughly to a feed control data and an auxiliary function data, the former of which is processed under interpolation arithmetic to be distributed to servomotors, the auxiliary function data being then transmitted to an auxiliary function control device 7 to instruct a functional operation corresponding thereto. The functional control device 7 is ordinarily constructed by relay circuits and performs a sequence control by activating a relevant relay in accordance with the auxiliary function data.
The BTR-adapters 4, 4 are connected by means of interface units 5, 5 with a data line 1a, which includes a plurality of data transfer lines for transferring data and a plurality of control signal lines for requesting and setting the data. The BTR-adapters 4, 4 are paired respectively with the numerical controllers 2, 2 for exclusive use, and each has a distinctive hard-wired construction. However, components of the BTR-adapter 4 often malfunction so that the operational reliability of the adapter 4 is lowered in proportion to the number of components. Further drawbacks are present because the design of the adapter 4 is quite time consuming and an increase in the number of components undesirably elevates the cost.
There is also known a programmable sequence controller which is used only to control the sequence operations of machines in lieu of relay circuits. For this reason, even where the sequence controller is employed in a computer controlled system for numerically controlled machine tools, the sequence controller only serves to control the sequence operations of the machine tool and the conveyer apparatus for conveying workpieces between the machine tools. Since it is possible to monitor the operational conditions of the machines, the sequence controller can perform a trouble diagnosis for the machines under the control of a computer 10 by being connected with the computer through an interface circuit 12, as illustrated in FIG. 2.
In FIG. 2, there is provided a magnetic disk 21 as an outer memory device which is connected with the computer 10 through an interface circuit 22. A teletypewriter 23, a paper-tape reader 24, and a display device 25 of a cathode ray tube type are also connected with the computer 10 respectively through interface circuits 26. Data lines to numerical controllers 16, 16 are provided separate from the data line to the sequence controller 13. Accordingly, such a BTR-adapter 17 as the foregoing and an appropriate data line have to be furnished for each unit of an individual machine tool 14, thus resulting in complicating the entire construction of the control system, raising the production cost, and prolonging the necessary term for design and production.
In FIG. 2, each of the machine control units 19, 19 is provided to control servomotors of the associated machine tool 14 upon receipt of interpolation data which is calculated by the computer 10 in accordance with well-known arithmetic methods, and is different from the numercial controller 16 in that it does not have an arithmetic function for the interpolation data. In this connection, the data which is fed from the computer 10 through an interface circuit 20 is different in its format from the data fed to the numerical controller 16. However, the present invention is applicable also to the system using the machine control units 19, 19 as well as that using the numerical controllers 16, 16.